Photo flash intensity control with variable resistor in flash tube discharge circuit

ABSTRACT

A system for controlling the extent to which flash illumination is provided during exposure of film in a camera. A preparatory flash and a main flash are provided with the system. Light from the preparatory flash is reflected from the object which is to be photographed to a photosensitive unit which responds to this reflected light for influencing the setting of a variable resistor whose setting is further influenced in accordance with additional exposure-determining factors, so that the variable resistor is set at a given value indicative of these exposuredetermining factors as well as the light reflected during the preparatory flash. With the information thus stored at the variable resistor in the form of the given value of the setting thereof, this variable resistor is operatively connected to the main flash for controlling the extent of flash illumination provided thereby during actual film exposure.

United States Patent Uno et al.

1541 PHOTO FLASH INTENSITY CONTROL WITH VARIABLE RESISTOR IN FLASH TUBEDISCHARGE CIRCUIT [72] Inventors: Naoyuki Uno, Oi-Machi, lruma-gun;Seijiro Tokutomi, Fujisawa, both of Japan [73] Assignees Asahi KogakuKogyo Kabushiki Kaisha, Tokyo-to, Japan [22 Filed: Sept. 10, 1970 21Appl.No.: 71,117

[30] Foreign Application Priority Data Sept. 22, 1969 Japan ..44/75483[52] US. Cl ..315/151, 95/1 1.5 R, 250/205, 315/156, 315/241 P, 315/245[51] Int. Cl. ..H05b 41/40 [58] Field of Search ..315/151, 152,154,156,159, 315/241 R, 241 P, 245; 95/10, 115 R;

[ 51 3,681,649 [451 Aug. 1,1972

3,465,656 9/1969 Wick etal. ..315/241;

Primary Examiner-Roy Lake Assistant Examiner-Siegfried H. GrimmAtt0rneySteinberg & Blake 5 7] ABSTRACT A system for controlling theextent to which flash illumination is provided during exposure of filmin a camera. A preparatory flash and a main flash are provided with thesystem. Light from the preparatory flash is reflected from the objectwhich is to be photographed to a photosensitive unit which responds tothis reflected light for influencing the setting of a variable resistorwhose setting is further influenced in accordance with additionalexposure-determining factors, so that the variable resistor is set at agiven value indicative of these exposure-determining factors as well asthe light reflected during the preparatory flash. With the informationthus stored at the variable resistor in the form of the given value ofthe setting thereof, this variable resistor is operatively connected tothe main flash for controlling the extent of flash illumination providedthereby during actual film exposure.

9 Claims, 2 Drawing Figures I? e-ZHUTTER BUTTON PHOTO FLASH INTENSITYCONTROL WITH VARIABLE RESISTOR IN FLASH TUBE DISCHARGE CIRCUITBACKGROUND OF THE INVENTION I tion of an object which is to bephotographed an artificial illumination derived from a flash tube,for'example. Conventionally, the operator of the camera will know of acertain guide number in accordance with the characteristics of the flashdevice, and in accordance with factors such as this guide number, thedistance of the camera to the object, and the film speed, the operatorwill set into the camera a given exposure aperture size, the exposuretime being predetermined and set at a given value for achieving propersynchronization of the film exposure with the flash illumination. Theseoperations require a considerable inconvenience and skill on the art ofthe operator, particularly when the settings indicated according tocalculations of this latter type are to be further modified by theexperience and intuition of the operator in accordance with theparticular conditions under which a photograph is made.

In view of the complications-resulting from these conventionalprocedures, it has already been proposed t provide an automated type offlash illumination, but the known automatic flash illuminating devicessuffer from several drawbacks. They are exceedingly expensive andcomplex. They require special components which are expensive. Thus, atruly satisfactory solution to the problem has not yet been achieved.

SUMMARY OF THE INVENTION It is accordingly a primary object of thepresent invention to provide an exceedingly simple but highly effectivesystem for achieving an automatic control of the flash illumination.

In particular, it is an object of the present invention to provide astructure which can achieve a precise automatic control of the flashillumination without requiring the introduction into the system of afactor such as the distance of the camera to the object.

In addition, it is an object of the invention to provide a constructionwhich is composed of relatively simple and inexpensive components whichwill operate very reliably to achieve the desired results.

Furthermore, it is an object of the invention to provide a constructionwhich can produce all of the required automatic operations simply inresponse to actuation of a shutter button to trip the shutter andinitiate an exposure.

Furthermore it is an object of the invention to provide a constructionof this type which is exceedingly compact so that it can be incorporatedin a highly effective manner into a camera without undesirablyincreasing the size or weight thereof.

According to the invention a preparatory flash means is provided forachieving a preparatory flash illumination and a main flash means isprovided for achieving a main flash illumination which is used duringactual exposure of the film. A photosensitive means receives lightreflected from the object during preparatory flash illumination, andthis latter photosensitive means together with a means for introducingadditional exposure-determining factors are operatively connected to avariable resistor means for setting the latter 4 at a given valueindicative not only of thev exposuredetermining factors but also of thelight intensity reflected from the object in response to the preparatoryflash illumination. When. the main flash means is operated to provideillumination during actual film exposure, the variable resistor means isoperatively connected with the main flash means to influence theoperation thereof so as to achieve a proper exposure.

BRIEF DESCRIPTION OF DRAWINGS The invention is illustrated by way ofexample in the accompanying drawings which form part of this applicationand in which:

FIG. 1 is a graph illustrating flash operation with different resistancevalues; and

FIG. 2 is a schematic wiring diagram of one example of a systemaccording to the present invention.

, DESCRIPTION OF PREFERRED EMBODIMENTS The present invention is basedupon the well known principle that the extent to which light is derivedfrom flash illumination, during discharge of a flash tube, diminishes asthe value of a resistor increases, where this resistor is connected inseries with the capacitor whose discharge energizes the flash tube.Thus, referring to FIG. 1 where the ordinate indicates light intensitywhile the abscissa indicates time, it will be seen that three curves areshown for three resistors R R and R The resistor R is of the smallestvalue while the resistor R is of the greatest value and the resistor Ris at a value between that of resistors R and R As is apparent from FIG.1, with the smallest resistance R, the greatest light intensity isachieved from a flash tube while with the largest resistance R thesmallest light intensity is achieved, and of course the intermediateresistor R gives an intermediate light intensity.

Thus, in accordance with the present invention there is operativelyconnected with a flash tube a variable resistor which is in series withthe flash tube to influence the operation thereof as illustrated by thegraph of FIG. 1. This variable resistor is set in accordance with anumber of factors so as to achieve a proper exposure from the flashillumination. One of these factors which determines the variableresistor is light reflected from the object which is to be photographedduring a preparatory flash which is the same as the main flashillumination except for the amount of the flash illumination which isfixed for the preparatory flash purposes but which will vary duringactual exposure in accordance with the setting of the variable resistor.

Referring to FIG. 2, there is schematically shown at the upper leftportion thereof a photosensitive means 1 capable of receiving lightreflected from the object which is to be photographed and providing in awell known manner a resistance value determined by the intensity of thelight received from the object which is to be photographed. Thisphotosensitive means 1 is connected in series with a variable resistor 2which forms a means for introducing additional exposure-determiningfactors. Thus the variable resistor 2 is set in a well known manner at avalue determined by the speed of the film which is exposed in thecamera, the setting of the diaphragm, and the exposure time. Theseseriesconnected components 1 and 2 are electrically connected betweenthe terminals A of a low-voltage current source which is notillustrated. A current-amplifying transistor 4 has its base connected tothe junction P between the photosensitive means 1 and the variableresistor 2. The emitter of the transistor 4 is connected in series withan integrating capacitor 5.

The transistors 6 and 7 provide a high-input impedance amplifyingcircuit with the base of the transistor 6 connected to the emitter ofthe transistor 4 and the capacitor 5, so that the components 4-7 form aninformation-memorizin g section.

According to one possible embodiment of the present invention, avariable resistor means is formed by a transistor 8 which has its baseconnected to the output terminal of the amplifying circuit 6, 7. Thecollector of the transistor 8 is electrically connected with a contact Mof a change-over switch 9 which is electrically connected with oneelectrode of a flash-discharge tube 10 which serves as a single flashtube for providing preparatory and main flash illumination. The othercontact S of the change-over switch 9 is electrically connected with apreparatory flash capacitor means 13 electrically connected through aswitch 12 in parallel with a main flash capacitor means 11 whichdischarges during the synchronized exposure when the film in the camerais exposed in synchronism with the main flash illumination. Thesedischarge capacitors 11 and '13 are in series with the flash tube 10.

In series with the capacitor 13 is a switch 14 which is interconnectedwith the switch 12 in such a way that when one of these switches is openthe other is necessarily closed. The switch 14 is a normally open switchwhile the switch 12 is a normally closed switch, and these switches arecontrolled from a relay in a manner described below.

A trigger transformer 15 is provided for initiating the operation of theflash tube 10 with the high voltage secondary winding of the transformer15 connected to an electrode of the flash tube 10 for initiating theoperation thereof. The primary winding of the trigger transformer 15 iselectrically connected with a main trigger capacitor 16 the charge ofwhich is used for initiating operation of the flash tube 10 through thetrigger transformer 15 in connection with main flash illumination. Inparallel with the main trigger capacitor 16 is a preparatory triggercapacitor 17, these capacitors being connected in parallel with eachother through a contact M of a change-over switch 18. This switch 18 hasa contact S which is engaged and becomes operative when preparatoryflash illumination is initiated through the preparator trigger capacitor17.

As is well known, at a given fraction of a second after the shutterbutton is depressed to trip the shutter and make the exposure, asynchronizing switch is closed for initiating the main flashillumination in synchronism with the tripping of the shutter to exposethe film, and for this purpose there is provided a synchronizing switch19 which has an X contact engaged by the switch 19 when the latter isclosed for providing the synchronized main flash illumination.

When the shutter button is depressed to initiate an exposure, a switch20 is automatically closed in response to depression of the shutterbutton, as schematically indicated at the upper part of FIG. 2. Thisswitch 20 serves to energize a timer 21 which in turn serves to maintaina relay 22 energized for a length of time determined by the timer 21.Thus, upon closure of the switch 20 by depression of the shutterbuttonthe timer 21 will maintain a supply of current to'the relay 22only until a given period of time has elapsed, after which the supply ofcurrent to the relay 22 is automatically terminated. Thisrelay 22 serveswhen energized to close a normally open current-source switch 3, andalso the change-over switches 9 and 18 which normally engage the contactM are moved into engagement with the contacts 8 respectively, inresponse to energizing of the relay 22. Also, in response to energizingof the relay 22 the normally closed switch 12 is opened while thenormally opened switch 14 is closed. These connections between the relayand the several relay-controlled switches are indicated schematically inFIG. 2. The switches may actually take the form of a gang of leafsprings carrying switch contacts which move into and out of engagementwith stationary contacts, and the distance between the stationary andmovable contacts of each switch can be chosen so that the switches willoperate in a given sequence with certain switches operating at shortintervals after other switches in a manner described in greater detailbelow.

The above-described structure operates in the following manner:

When the shutter button is depressed to close the switch 20, thecharging of the several capacitors has already been completed. Thus, thecharging of the main flash capacitor 11, the preparatory flash capacitor13, and the trigger capacitor 16 and 17 has been completed prior toclosing of the switch 20 by depression of the shutter button. Thisswitch 20 will thus close when the shutter is tripped in order toinitiate an exposure. The closing of the switch 20 of course starts therunning of the timer 21 and the relay 22 will remain energized duringthe time determined by the timer 21. Upon energizing of the relay 22 theswitch 12 is opened, the switch 14 is simultaneously closed, and thecurrent-source switch is closed. Very shortly thereafter, because of thegap between the stationary, movable contacts of the switch 9, thechange-over switch 9 is changed over from its normalpositi'on engagingthe contact M to its position engaging the contact S. Also, shortlyafter actuation of the above switches the switch 18 engages the contactS.

These switch operations provide a discharge through the preparatoryflash trigger capacitor 17 so as to actuate the transformer 15 toinitiate the operation of the flash tube 10 which now acts as thepreparatory flash means. Thus, the discharge of the capacitor 17 actsthrough the high-voltage secondary winding of the transformer 15 to acton the electrode connected to this secondary winding for initiating theoperation of I the flash tube 10. At this time the closed switch 14 con-As a result of this preparatory flash illumination, the light therefromwill be reflected from the object which is to be photographed to thephotosensitive means 1. The variable resistor 2 has of course beenpreviously set to introduce the additional exposure-determining factorsof the film speed, exposure time, and exposure aperture. The dividedvoltage from the current source resulting from the resistance values ofthe components 1 and 2 is appliedto the base of the current-amplifyingtransistor 4. The resulting amplified current charges the integratingcapacitor 5, and the extent of charge thereof corresponds to theintegrated value of the light reflected from the object to bephotographed as a result of the preparatory flash while also includingany normal or natural light which is reflected. The voltage across theterminals of the capacitor 5 resulting from the charging thereof isapplied through the high-input impedance amplifying circuit formed bythe transistors 6 and 7 to the base of the transistor 8 which forms thevariable resistor means, and thus this influencing of the transistor 8serves to set the internal resistance thereof at a value which isindicative of the exposure-determining information including the factorsof light reflected from the object due to the preparatory flash and thevarious other exposure-determining factors. This influence of thevariable resistor means 8 sets the latter at a given resistance valuewhich is subsequently used for controlling the main flash illumination.

The above operations are completed within a time period starting fromthe actuation of the relay 22, with all of the operations taking placewithin a period of I I within 5 ms, so that after elapse of period oftime on the order of 5 ms, the timer 21 will terminate the energizing ofthe relay 22. The termination of the supply of current to the relay 22after this period of time will thus take place after the aboveinformation has been memorized and retained in the form of theparticular setting of the variable resistor means 8.

Upon termination of the energizing of the relay 22, the switch 3 opens,the change-over switches 9 and 18 return to the contact M, respectively,and the switch 14 opens while the switch 12 simultaneously closes.Therefore, the memorized information indicated by the value of theinternal resistance of the transistor 8 is connected through thevariable resistor means 8 in series with the flash tube 10 and the maindischargecapacitor 11. Thus, the memorized information is applied to thebase of the transistor 8 so that the internal resistance thereof has agiven value corresponding to the memorized information.

At this time the switch 19 will engage the X contact so as to close thecircuit through the main trigger capacitor 16 which now acts through thetrigger transformer 15 on the discharge tube 10 for initiating theoperation thereof, and now the discharge will take place from the maindischarge capacitor 11. However, as is apparent from FIG. 1 and theabove discussion the extent of illumination derived from the main flashmeans at this time will be determined by the setting of the variableresistor means 8. Thus, the resulting flash will provide an amount oflight determined by the internal resistance value of the transistor 8acting as a seriesconnected resistor operatively connected with theflash tube 10. In this way a proper exposure of the film is achieved ina fully automatic manner.

Thus, with the structure of the invention the preparatory flash providesthe light reflected from the object to serve as part of the setting ofthe variable resistor means which is connected in series with the flashdischarge tube, and this setting is automatically achieved. Therefore,such adjusting operations as might be required for introducing suchexposure-determining factors as the distance of the camera to the objectfor a given intensity of flash are not at all required with the presentinvention. Therefore, the exposure control operations for achieving asynchronized flash exposure is considerably simpler than is achievedwith conventional flash apparatus capable of providing an automaticcontrol of the amount of exposure light. The entire arrangement of theinvention is considerably simpler than conventional structures, so thatthe structure of the invention is a great practical significance.

It is to be noted that while the variable resistor means has beendisclosed above as taking the form of a transistor whose internalresistance is set at a given value, it is also possible to connect inseries with the flash tube 10 a variable resistor whose setting isadjusted from a servo-motor, actuated in accordance with the memorizedinformation.

What is claimed is:

1. For use with a camera, preparatory flash means for providingpreparatory flash illumination, photosensitive means for receiving froman object which is to be photographed light reflected from the object,variable resistor means operatively connected with said photosensitivemeans to be set thereby at a value influenced by the light received bysaid photosensitive means in response to said preparatory flash means,means operatively connected with said variable resistor means foradditionally influencing the latter according to additionalexposure-determining factors, so that said variable resistor means isset at a given value indicative of the light reflected from the objectin response to the preparatory flash illumination and the additionalexposure-determining factors, main flash means for providing flashillumination during exposure of film in the camera, and connecting meansfor connecting said variable resistor means to said main flash meansafter said variable resistor means has been set at said given value andfor maintaining said variable resistor means operatively connected withsaid r'nain flash means during operation of the latter, so that the mainflash means is regulated to provide a proper exposure.

2. The combination of claim 1 and wherein said variable resistor meansis a transistor having an internal resistance set at said given value. 4

3. The combination of claim 1 and wherein said preparatory and mainflash means include a single flash tube and a pair of triggeringcircuits one of which is a preparatory triggering circuit for actuatingsaid single flash tube to form said preparatory flash means and theother of which is a main triggering circuit for actuating said flashtube to provide said main flash means.

4. The combination of claim 3 and wherein said variable resistor meansis a transistor having an internal resistance which assumes said givenvalue.

5. The combination of claim 4 and wherein said means for influencingsaid variable resistor means according to additionalexposure-determining factors includes a variable resistor connected inseries with said photosensitive means.

6. The combination of claim and wherein a junction interconnects saidvariable resistor forming said means for introducing said additionalexposure-determining factors and said photosensitive means, acurrent-amplifying transistor connected with said junction,

and an integrating capacitor operatively connected transistor whichforms said variable resistor means to said flash tube only when thelatter provides the main flash illumination, a preparatory flashcapacitor connected with said flash tube for providing a dischargethrough the latter during preparatory flash illumination, said switchconnecting said flash tube into the circuit of said preparatory flashcapacitor during preparatory flash illumination.

9. The combination of claim 8 and wherein a main flash capacitor isprovided for discharging through said flash tube, during main flashillumination, and additional switch means for connecting said main flashcapacitor to said flash tube while said variable resistor means isconnected in series therewith.

1. For use with a camera, preparatory flash means for providingpreparatory flash illumination, photosensitive means for receiving froman object which is to be photographed light reflected from the object,variable resistor means operatively connected with said photosensitiVemeans to be set thereby at a value influenced by the light received bysaid photosensitive means in response to said preparatory flash means,means operatively connected with said variable resistor means foradditionally influencing the latter according to additionalexposure-determining factors, so that said variable resistor means isset at a given value indicative of the light reflected from the objectin response to the preparatory flash illumination and the additionalexposure-determining factors, main flash means for providing flashillumination during exposure of film in the camera, and connecting meansfor connecting said variable resistor means to said main flash meansafter said variable resistor means has been set at said given value andfor maintaining said variable resistor means operatively connected withsaid main flash means during operation of the latter, so that the mainflash means is regulated to provide a proper exposure.
 2. Thecombination of claim 1 and wherein said variable resistor means is atransistor having an internal resistance set at said given value.
 3. Thecombination of claim 1 and wherein said preparatory and main flash meansinclude a single flash tube and a pair of triggering circuits one ofwhich is a preparatory triggering circuit for actuating said singleflash tube to form said preparatory flash means and the other of whichis a main triggering circuit for actuating said flash tube to providesaid main flash means.
 4. The combination of claim 3 and wherein saidvariable resistor means is a transistor having an internal resistancewhich assumes said given value.
 5. The combination of claim 4 andwherein said means for influencing said variable resistor meansaccording to additional exposure-determining factors includes a variableresistor connected in series with said photosensitive means.
 6. Thecombination of claim 5 and wherein a junction interconnects saidvariable resistor forming said means for introducing said additionalexposure-determining factors and said photosensitive means, acurrent-amplifying transistor connected with said junction, and anintegrating capacitor operatively connected with an emitter of saidcurrent-amplifying transistor and connected to said transistor whichforms said variable resistor means.
 7. The combination of claim 6 andwherein a transistorized amplifier is connected between said integratingcapacitor and a base of said transistor of said variable resistor means.8. The combination of claim 7 and wherein said connecting means includesa switch connecting said transistor which forms said variable resistormeans to said flash tube only when the latter provides the main flashillumination, a preparatory flash capacitor connected with said flashtube for providing a discharge through the latter during preparatoryflash illumination, said switch connecting said flash tube into thecircuit of said preparatory flash capacitor during preparatory flashillumination.
 9. The combination of claim 8 and wherein a main flashcapacitor is provided for discharging through said flash tube duringmain flash illumination, and additional switch means for connecting saidmain flash capacitor to said flash tube while said variable resistormeans is connected in series therewith.